Pulp containers with a threaded part which are prepared by forming a thread on a paper cylinder by a calender press are known. However, the shapes of the threads and containers formed by a calender press are limited in nature of the method adopted only to provide a poor seal with a cap, allowing the contents to leak during use. In addition, the paper cylinder itself is not strong enough to assure durability for repeated capping and uncapping.
JP-A-8-302600 discloses a pulp molded article having on its surface a projection such as a thread. The projection is attached with an adhesive, etc. in a separate step or formed in the step of drying a molded article. The method of forming a projection in the step of drying is advantageous for efficient production of molded articles since the step of making a projection and the step of attaching the projection are carried out on the same molding line. Where a projection is formed in a drying step, however, cases are met with, while depending on the shape of the projection, in which the depression on the molding surface of a mold is not accurately transferred only to make a rounded projection or a projection with a rough surface, or the resulting projection fails to have an increased density for securing sufficient strength.